Forming of thin metal filaments

ABSTRACT

This disclosure deals with an apparatus and process for forming thin metal filaments from liquid metal. An electrically conductive metal is placed in a crucible having an opening therein, the metal either having been previously heated to a liquid state or being so heated while in the crucible. A coil is positioned adjacent the metal and a current pulse is passed through the coil. The current flow generates an intense magnetic field which compresses or squeezes the metal, causing the metal to be forced out of the magnetic field through the opening in the crucible in the form of an elongated filament.

United States Patent 72] Inventor James W. Halley Chesterton, Ind. [21] Appl. No. 832,201 [22] Filed June 11, 1969 [45] Patented May 25, 1971 [73] Assignee Inland Steel Company Chicago, Ill.

[54] FORMING 0F THIN METAL FILAMENTS 12 Claims, 4 Drawing Figs. [52] US. Cl 2l9/7.5, 219/149 [5 I 1 Int. Cl 1105b 5/00 [50] Field of Search 219/75, 149; 72/706 [56] References Cited UNITED STATES PATENTS 2,552,876 5/1951 Tama 417/50X 2,686,864 8/1954 Wroughton et al. 219/7.5

Primary Examiner-J. V. Truhe Assistant Examiner-Hugh D. Jaeger Att0rney-Hibben, Noyes & Bicknell ABSTRACT: This disclosure deals with an apparatus and process for forming thin metal filaments from liquid metal. An electrically conductive metal is placed in a crucible having an opening therein, the metal either having been previously heated to a liquid state or being so heated while in the crucible. A coil is positioned adjacent the metal and a current pulse is passed through the coil. The current flow generates an intense magnetic field which compresses or squeezes the metal, causing the metal to be forced out of the magnetic field through the opening in the crucible in the form of an elongated filament.

1 F ORMING F THIN METAL FILAMENTS DISCLOSURE It is difficult to form very small diameter metal filaments or fibers of the type used as a reinforcing or as a control wire in a military rocket guidance system. Such filaments having a diameter of the order of 0.001 inch have been formed by a drawing process, but such a process is difficult and expensive partly because it has been necessary to use diamond dies.

The present invention deals with an improved lower cost apparatus and process for forming thin metal filaments. Apparatus embodying the invention comprises a container for receiving a quantity of electrically conductive liquid metal, the container having an open side, an electric coil positioned adjacent the container and the metal, and an electric circuit connected to the coil for passing a current pulse through the coil. The magnetic field resulting from the flow of current applies pressure on the liquid metal and squeezes the metal out of the open side of the container in the form of a thin filament. The coil is preferably shaped to produce a magnetic field which gradually increases in strength with distance toward the opening. Means may also be provided to heat the metal while it is in the container, and additional'means may be provided to cool the filament as it leaves the container.

Objects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures of the drawing, in which:

FIG. 1 is a view illustrating schematically an apparatus embodying the invention;

FIG. 2 isa view similar to FIG. 1 but showing a different position of the parts of the apparatus;

FIG. 3 is a sectional view taken on the line 3-3 of FIG. 1'; and

FIG. 4 is an enlarged sectional view taken on the line 44 of FIG. 3.

Apparatus embodying the invention comprises a generally cup-shaped container or crucible which is preferably made of a refractory material and which is supported on a base 11'. With particular reference to FIG. 4, the crucible 10 includes a sidewall 12, a bottom wall 13, and an upper open side which is indicated at 14. While it is not necessary, the cross section of the crucible 10 may be circular as shown in FIG. 3, and the wall 12 may taper upwardly and radially inwardly.

Positioned coaxially around the crucible 10 is an electric conductor 16, made of a material such as copper, which, in the present instance, makes substantially one turn or loop around the crucible 10. With reference to FIGS. 1 and 3, the ends of the conductor 16 are connected to a pair of power leads 17 and 18, the lead 17 being located adjacent the lower edge of the conductor 16 and the other lead 18 being located adjacent the upper side of the conductor. The conductor 16 is preferably made relatively thick and sturdy so that a large surge of current may be passed through it with relatively little power loss and with relatively little change in the configuration of the conductor due to the force of the magnetic field generated by the current.

Connected to the power leads l7 and 18 is an electric circuit (FIG. 1) for passing a heavy surge of current through the conductor 16. In the present instance, the circuit includes a bank of capacitors indicated schematically at 21, and a DC charging circuit 22. The circuit 22 may comprise an AC to DC rectifier and means for stepping up the power transmission line voltage. The capacitor bank 21 is connected across the power leads l7 and 18 in series with a switch 23, and the charging circuit 22 is connected across the capacitor bank 21. Another switch 24 is connected in series with the charging circuit 22 so that the charging circuit may be selectively connected to the capacitor bank 21. Thus, when the switch 23 is open and the switch 24 is closed, the capacitor bank 21 will be charged by the circuit 22, and when the switch 24 is open and switch 23 is closed, the capacitor bank 21 will be discharged through the conductor 16. The switch 23 is preferably a very fast acting switch such as an electronic switch.

During operation of the apparatus, a quantity of electrically conductive liquid or molten metal, such as steel or aluminum, indicated by the numeral 26 in FIGS. 2 and 4, is placed in the crucible 10. To facilitate loading of the metal 26 into the crucible 10, the base 11 and the conductor 16 are preferably made movable relative to each other, and, in the present instance, the erucible 10 is movable and the conductor 16 is held stationary. Such movement may be accomplished by a hydraulic mechanism 27 including a cylinder 28 and a piston rod 29 which is secured to a piston within the cylinder 28. The axis of the rod 29 is coaxial with the crucible l0 and with the conductor 16, and the outer end of the rod 29 is secured to the base 11 by a coupling 31. Two lengths 32 and 33 of hose eonnect the opposite ends of the cylinder 28 to a source of hydraulic fluid under pressure so that the rod 29 may be moved into and out of the cylinder 28. Thus, the support base 11 and the crucible 10 secured thereto may be moved up and down relative to the conductor 16. When the crucible 10 is lowered away from the conductor 16 to the position shown in FIG. 2 the crucible 10 may be charged with liquid metal 26, and when the crucible 10 is moved upwardly to the position shown in FIG. 1, the crucible 10 and the liquid metal 26 are encircled by the conductor 16.

As will be explained hereinafter, the liquid metal 26 is forced out of the crucible 10 in the form of a thin filament, and means is preferably provided to cool the filament as it leaves the crucible 10. Such means comprises a ring-shaped tube 38 positioned coaxially with the crucible 10 and closely adjacent the margin of the opening 14. The inner periphery of the tube 38 has a plurality of holes 39 (FIG. 4) formed therein and a conduit 41 (FIG. 1) connects the interior of the tube 38 to a supply 42 of a cool fluid. The fluid is preferably an inert gas such as nitrogen which will not cause oxidation of the metal filament leaving the crucible 10. Gas leaving the supply 42 flows through the tube 38 and out of the holes 39 toward the axis of the crucible 10 in the form of a number of small jets.

The metal 26 within the crucible 10 preferably has a temperature which is just above the freezing point of the metal. The metal may be heated to this temperature prior to placing it in the crucible 10, but it is preferred that heating means also be provided adjacent the crucible 10 for heating the metal 26 and maintaining the metal at the proper temperature while it is in the crucible 10. In the present instance, such heating means comprises an induction heater including a circular coil 46 (FIG. 2) which is connected to an alternating current power supply 47 by a pair of conductors 48. A variable resistor 49 is connected in one of the conductors 48 so that the amount of power delivered to the coil may be adjusted. The coil 46 is preferably displaced from the conductor 16 at the time that the surge of current is passed through the conductor 16 so that the intense magnetic field set up by the conductor 16 will not damage the coil 46. This may be accomplished by fixing the coil 46 in place at the location shown in FIG. 2 where it encircles the metal 26 only when the crucible 10 is in its lower position, or the coil 46 may be made movable with the crucible 10 between the solid and dashed line positions shown in FIG. 1. In the former construction the coil 46 would heat the metal 26 only when the crucible is in its lower position and in the latter construction the coil 46 would heat the metal 26 in both positions of the crucible but would be moved downwardly away from the conductor 16 just prior to the time that the switch 23 is closed.

The crucible 10 should be made of a nonconducting refractory material such as silica or alumina, which will not be influenced by the magnetic field set up by current flow through the conductor 16, and the base 11 and the tube 38 are preferably also made of such a material. The conductor 16 preferably tapers upwardly and radially inwardly as shown in FIG. 4 so that the intensity of the magnetic field is greatest adjacent the opening 14 and gradually decreases in the direction of the bottom wall 13. Such a configuration of the conductor is advantageous because it thins down the metal to a small diameter filament as it leaves the crucible 10. The wall 12 of the crucible 10 may have a corresponding taper as shown in H6. 4 but this is not necessary. The bottom wall 13 of the crucible 10 is preferably made relatively thick and sturdy so that it can withstand the forces encountered during operation.

Considering the operation of the apparatus, a quantity of liquid or molten metal 26 is placed inthe crucible 10 as by lowering the base 11 and the crucible 10 to the position shown in FIG. 2 and placing the metal in the crucible 10. The hydraulic mechanism 27 is then actuated to raise the crucible 10 to the position shown in FIGS. 1 and 4 where the crucible l and the metal 26 are located within the loop of the conductor 16.

Y The coil 46 may be employed to maintain the temperature of the metal 26 at the point where it is just above freezing. With the switch23 open, the switch 24 is closed and the charging circuit 22 charges the capacitor bank 2!. After the capacitor bank 21 is charged, the switch 24 is opened and the switch 23 is closed, thereby connecting the capacitor bank 21 across the conductor 16. In accordance with magnetic-pulse forming theory, the surge of current-flowing through the conductor 16 creates an intense magnetic field within the crucible 10, and the field induces current flow in the electrically conductive metal 26. The interaction between the current flow in the metal 26 and, the magnetic field generated by the current flow through the conductor 16 causes a radially inwardly directed force to be exerted on the metal 26. This force squeezes the liquid metal 26 inwardly toward the center line or axis of the conductor 16'. The bottom wall 13 of the crucible l0 prevents the liquid metal 26 from being squeezed downwardly, but the metal may be squeezed upwardly, as shown at 51 in FIG. 4, because there is not force against its movement in this direction. The gradually increasing magnetic field causes the metal to thin down to a filament as it moves upwardly, andthe jets or streams of gas leaving the holes 39 strike the metal and cool it to form a filament 52 as the metal leaves the crucible. A

device may be provided to catch the filament after it has left the crucible, or the filament may be permitted to fall 'on the floor or other support for the apparatus. The crucible l0 and the conductor 16 may be positioned either vertically or at a slight angle from the vertical, and in the present instance they are generally vertical. After afilament has been formed as described, the foregoing steps may be repeated a number of times in order to produce a lclaimz, t 1. Apparatus for forming a thin filament from a liquid elecplurality of filaments. v

trically conductive metal, comprising a coil, means for supporting a quantity of said liquid metalwithin the loop of said coil, and means for passing a surge of current through said coil cooling said filament as it leaves said magnetic field.

3. Apparatus as in claim 1, wherein said metal is squeezed out of said field along the axis of said coil, and the size of said loop decreases in the'direction in which said filament is forced in order to thin down said filament.

4. Apparatus for forming a metal filament, comprising a container adapted to support a quantity of electrically conductive liquid metal, said container having a generally upwardly facing opening therein, an electrical conductor positioned adjacent said container and shaped to produce an intense magnetic field around said metal when a surge of current flows through said conductor, said magnetic field exerting a compressive force on said metal and said force being directed inwardly toward a line which extends through said opening, and circuit means connected to said conductor for passing a surge of current through said conductor of such intensity that the resulting magnetic field compresses the metal within said container and forces the metal along said line out of said container in the form of an elongated filament. I

5. Apparatus as in claim 4, wherein said conductor substantially encircles said quantity of metal and forms a loop.

' 6. Apparatus as in claim 5, wherein the diameter of said logp gradually tapers inwardly and toward said opening.

. pparatus as in claim 4, and further including cooling means adjacent said opening for directing a relatively cool fluid against said filament as said filament leaves said container in order to rapidly cool and solidify said filament.

8. Apparatus as in claim 4, and further including means for heating said metal while said metal is in said container.

9. Apparatus as in claim 5, wherein said conductor also substantially encircles said container.

10. Apparatus for forming a metal filament from an electrically conductive metal, comprising a generally cup-shaped container having an opening on the upper side thereof, a coil positioned around and generally coaxial with said container, said coil being elongated in the direction of the axis of said container and tapering radially inwardly and upwardly toward said opening, and circuit means connected to said coil for passing a surge of current through said coil of such intensity to generate an intense magnetic field which compresses the metal toward said axis, such compression causing the metal to be squeezed upwardly along saidaxis and out of said opening in the form of an elongated filament.

' 11. Apparatus as in claim '10, and further including cooling means at the upper edge of said opening for directing a relatively cool fluid against said filament as it emerges from said container through said opening.

12. Apparatus as in claim 10, and further including means supporting said container for movement relative to said coil so that said metal may be placed in said container when said container is displaced from said'coil. 

1. Apparatus for forming a thin filament from a liquid electrically conductive metal, comprising a coil, means for supporting a quantity of said liquid metal within the loop of said coil, and means for passing a surge of current through said coil to generate magnetic field around said metal of such intensity that said field squeezes said metal out of said field in the form of a long thin filament.
 2. Apparatus as in claim 1, and further including means for cooling said filament as it leaves said magnetic field.
 3. Apparatus as in claim 1, wherein said metal is squeezed out of said field along the axis of said coil, and the size of said loop decreases in the direction in which said filament is forced in order to thin down said filament.
 4. Apparatus for forming a metal filament, comprising a container adapted to support a quantity of electrically conductive liquid metal, said container having a generally upwardly facing opening therein, an electrical conductor positioned adjacent said container and shaped to produce an intense magnetic field around said metal when a surge of current flows through said conductor, said magnetic field exerting a compressive force on said metal and said force being directed inwardly toward a line which extends through said opening, and circuit means connected to said conductor for passing a surge of current through said conductor of such intensity that the resulting magnetic field compresses the metal within said container and forces the metal along said line out of said container in the form of an elongated filament.
 5. Apparatus as in claim 4, wherein said conductor substantially encircles said quantity of metal and forms a loop.
 6. Apparatus as in claim 5, wherein the diameter of said loop gradually tapers inwardly and toward said opening.
 7. Apparatus as in claim 4, and further including cooling means adjacent said opening for directing a relatively cool fluid against said filament as said filament leaves said container in order to rapidly cool and solidify said filament.
 8. Apparatus as in claim 4, and further including means for heating said metal while said metal is in said container.
 9. Apparatus as in claim 5, wherein said conductor also substantially encircles said container.
 10. Apparatus for forming a metal filament from an electrically conductive metal, comprising a generally cup-shaped container having an opening on the upper side thereof, a coil positioned around and generally coaxial with said container, said coil being elongated in the direction of the axis of said container and tapering radially inwardly and upwardly toward said opening, and circuit means connected to said coil for passing a surge of current through said coil of such intensity to generate an intense magnetic field which compresses the metal toward said axis, such compression causing the metal to be squeezed upwardly along said axis and out of said opening in the form of an elongated filament.
 11. Apparatus as in claim 10, and further including cooling means at the upper edge of said opening for directing a relatively cool fluid against said filament as it emerges from said container through said opening.
 12. Apparatus as in claim 10, and further including means supporting said container for movement relative to said coil so that said metal may be placed in said container when said container is displaced from said coil. 